1. Field of the Invention
The present invention relates to an integrated circuit tester that tests an integrated circuit by applying a timing axis signal for testing.
2. Description of the Related Art
Timing axis signals output by an integrated circuit tester (xe2x80x9cIC testerxe2x80x9d) used to test integrated circuits are classified according to the number of pins on the integrated circuit (for example, 1024 pins), and deviations in the timing axis (xe2x80x9cskewxe2x80x9d) of these timing axis signals must be minimized as far as possible in order to increase the precision of the measurement. That is, at each pin of the integrated circuit, or specifically, at the pin contact point of the IC socket, etc., on which the semiconductor integrated circuit is mounted, the skew of the applied timing axis signals must be zero.
At the same time, the external dimensions of recent integrated circuits are being reduced in size, and in order to carry out testing of these integrated circuits using a conventional oscilloscope, a ground (or earth) is necessary. However, there are the problems that protecting the area for fabricating the ground pattern is difficult, and that with an oscilloscope, the testing probe may influence the timing axis signal applied to the integrated circuit because this test probe electrically contacts the electrode pad bound with a microstrip line when the signal detection is carried out. In addition, in order for the probe to make contact, electrode pads and seats that occupy a large area must be provided, and this interferes with reducing the size of the integrated circuit.
In consideration of the above-described problems, it is an object of the present invention to provide an integrated circuit tester that can supply a timing axis signal for testing that exhibit no time axis deviation at any pin by transforming the change in the electrical field of the device under test into optical properties of an element, uses an electro-optic probe such as an EOS that can extract the changes in these optical characteristics as an indirect electrical signal, detects the timing axis signal applied to each pin of the integrated circuit without direct electrical contact at a skew measurement point, and applies and controls a timing axis signal that cancels the phase differences on the microstrip line bound to each pin of the integrated circuit according to the detected output of the phase difference between this timing axis signal and a reference signal.
In order to attain the object, according to a first aspect, the integrated circuit tester provides microstrip lines that connect to a plurality of contact points of the device under test and supply timing axis signals for testing them; an electro-optic probe that is in proximity to these contact points, uses positions that are equidistant therefrom or pre-set distances therefrom as skew measurement points, and detects the timing axis signals on each microstrip line at these skew measurement points; and a phase detection means that detects the phase of the timing axis signals that this electro-optic probe detects; and wherein: a phase difference calculation means finds the phase difference between the phase detected by this phase detection means and the pre-set reference value, and a phase control means carries out phase control of the timing axis signals supplied to the microstrip lines so that the phase differences obtained by this phase difference calculation means are cancelled.
In addition, according to a second aspect, in this integrated circuit tester, the phase difference obtained by the phase difference calculation means is the value obtained under the condition that there is an equal distance from each contact point of the device under test to each skew measurement point.
In addition, according to a third aspect, in this integrated circuit tester, the value to be used is obtained by compensating the phase difference obtained by this phase difference calculation means based on a database value of the corresponding skew measurement point in the case that the distances from the contact points of the device under test to the skew measurement points are not identical.
In addition, according to a fourth aspect, in this integrated circuit tester, the skew measurement points used by the electro-optic probe are set on an insulating film applied to the microstrip line or a strip line having a part thereof exposed from this insulating film.
In addition, according to a fifth aspect, in this integrated circuit tester, a probe moving means is provided that moves the electro-optic probe according to the database value of the skew measurement point.